1. Field of the Invention
The present invention relates generally to portable video playback devices, and more particularly to portable digital video disc (DVD) playback devices.
2. Description of the Related Art
Prior to the advent of digital video technology, video information was recorded and transmitted as analog electrical signals. While analog video transmitters, receivers, and combination playback/record machines such as video cassette recorders (VCRs) can be built inexpensively, analog video is hard to search, edit, sort or enhance. In addition, pre-recorded analog media such as video cassettes for VCRs are rather expensive to produce and distribute.
There has been a rapid evolution from analog video technology to digital video technology, mainly because of the advantages that digital video has to offer. Digital video can be stored and distributed more cheaply than analog video mainly because digital video can be stored on randomly accessible media such as magnetic disc drives (hard disks) and optical disc media known as compact discs (CDs). Once stored on a randomly accessible media, digital video may become interactive, allowing it to be used in games, catalogs, training, education, and other applications. Even movies, which have traditionally been a chronologically linear media, may become interactive, allowing viewers to select their point of view, a plot path and the ending of the movie.
One of the newest products to be based on digital video technology is the digital video disc, sometimes called “digital versatile disc” or simply “DVD.” These discs are the size of an audio CD, yet hold up to 17 billion bytes of data, 26 times the data on an audio CD. DVD storage capacity (17 Gbyte) is much higher than CD-ROM (600 Mbyte) and a DVD can deliver the data at a higher rate than CD-ROM.
With the help of MPEG and Dolby compression technologies, a DVD can hold hours of high quality audiovisual content. DVD technology is predicted to be the eventual replacement for VCR technology, as well as a replacement for interactive multimedia applications currently based on CD-ROM technology. The enormous capacity of DVDs allows up to four feature-length movies to be stored on a single disc, with audio and video quality that is superior to that offered by other video formats.
A DVD looks like a conventional CD. More specifically, a DVD is made up of a reflective aluminum foil encased in a clear plastic. Like a CD, data is recorded on the disc in a spiral trail of tiny pits, and the discs are read using a laser beam. The DVD's larger capacity is achieved by making the pits smaller and the spiral tighter, and by recording the data in as many as four layers, two on each side of the disc. The pits of a DVD are formed in the foil by stamping it with a glass master. In the case of a single-sided DVD, the stamped disc is backed by a dummy, which may contain graphics advertising the contents of the disc. For a double-sided disc, two halves, each with their foil full of data, are bonded back to back.
While any kind of digital data can be distributed on a DVD, the first application of this new medium has been full-length feature movies. As a movie medium, DVD has many advantages over today's VHS tapes and laser discs. One advantage is that both the video and multi-channel audio produced by DVDs are superior to those possible with current technologies. Another advantage is that DVD will be the first digital medium to present movies in wide-screen format.
Because DVD is a random access device, it is possible for the player mechanism to seek to any place on the disc and begin playing. It can also pause, play in slow motion or fast forward easily, and with a much clearer picture than available from a tape player. These random access features allow an unlimited number of possible applications, from multiple endings for a movie, to interactive video games, to multiple camera angles.
In its raw state, digital video is so voluminous that a feature-length movie would require 40 DVDs at 4.7 billion bytes each. Fortunately, digital video in its raw state is comprised mostly of redundancies, i.e. elements that are the same or nearly so, which can be identified and removed. This process is referred to as compression (or sometimes “encoding”) and can eliminate over 97 percent of the data required to represent the video without noticeably affecting image quality.
DVD technology uses the MPEG-2 digital video compression standard. More particularly, to deliver the high image quality of DVD while fitting a movie into the 4.7 gigabyte capacity of a single DVD layer, a process called “variable bit rate encoding” is used. MPEG encoding compresses video by eliminating redundancies. The average data rate for video on a DVD is about 3.7 million bits per second. To provide superior sound, DVDs incorporate either Dolby's AC-3 Surround Sound or MPEG-2 audio. AC-3 or “Dolby Digital” provides six channels and MPEG-2 provides up to eight, each channel completely separate from the others.
DVD players include a motor that spins the disc, and a laser that reads information from the disc. The laser uses visible red light (as opposed to an audio CD player's infrared laser) to “read” the pits etched in the disc. These laser pulses are translated into electrical form by a digital signal processor (DSP), which is one type of integrated circuit. DVD players also include a digital decoder and a microcontroller.
The digital audio/video decoder is an integrated circuit that reconstitutes the compressed data on the disc, converting it into studio-quality video and CD-quality audio for output to TVs and stereo systems. The microcontroller controls the operation of the player, translating user inputs from the remote control or front panel into commands for the audio/video decoder and the disc reader mechanism. The microcontroller is also responsible for such operations as implementing parental lockout, dialing distributors for access codes and controlling decryption.
In summary, DVD technology represents a tremendous improvement in video and audio quality over traditional systems such as televisions, VCRs and CD-ROM. However, the technology has been difficult to utilize in part because DVD players are typically large, cumbersome devices that are difficult to transport. Furthermore, because DVD players must be operationally attached to a video display, such as a television or television monitor, they are virtually impossible to use anywhere space is limited, such as in a car or on an airplane.
Furthermore, prior art mobile video systems suffer from a large number of annoying problems. Hand-held and mobile television sets typically exhibit reception maladies such as RF multipath interference and poor or erratic signal strength in rural areas. Integrated TV/VCR combo units can counter these problems by providing tape playback capability, but they tend to be physically large and not truly portable. In view of the forgoing, it is desirable to have a portable DVD player capable of being easily transported and being used under a wide variety of conditions.